An electric arc furnace is an electrically operated furnace used for melting metal and/or for cleaning slag. The operation of the furnace is based on an arc flame that burns either between separate electrodes, or between electrodes and the material to be melted. The furnace may be operated either by AC or DC current. Heat is created in the arc flame, and also in the material to be melted, in case the arc flame burns between the material and the electrodes. Power is conducted to vertical electrodes that are located symmetrically in a triangle with respect to the midpoint of the furnace. In the case of a DC smelting furnace there is one electrode in the middle of the furnace. The assembly depth of the electrodes in the furnace is continuously adjusted, because they are worn at the tips owing to the arc flame.
The lower part of the electrode column assembly comprises a contact shoe ring, a pressure ring and a heat shield. The contact shoe ring consists of a plurality of contact shoe elements arranged as a ring to be in contact with a steel mantle inside of which the electrode paste is sintered. Such an electrode is a so-called Söderberg electrode. The contact shoe elements conduct electric current to the electrode. A pressure ring is arranged on the outside of the contact shoe ring, so that the contact shoe ring is surrounded by said pressure ring. The pressure ring consists of a plurality of pressure blocks connected with each other as a ring, which pressure blocks being provided with hydraulic bellows by which the contact shoes in the contact shoe ring are pressed against the steel mantle of the electrode. A heat shield surrounding the electrode column assembly is arranged above the pressure ring in the axial direction of the electrode column assembly. Also the heat shield is comprised of a plurality of segments connected with each other to form an assembly of annular form.
As mentioned above, the pressure ring consists of a plurality of pressure blocks connected with each other as a ring. The pressure blocks are commonly made of massive copper elements and they are provided with bellows with which a pressing force towards the contact shoes is created to press said contact shoes against the electrode. The bellows are maintenance free without any moving parts. However, if dust can penetrate between the bellows it may get bogged down. Also hot furnace gases can cause damage to the bellows cylinder or hydraulic fluid contained therein. With further reference to prior art document EP1971190 shows a pressure ring assembly in which the pressure blocks or pressure ring segments are provided with piston arrangements and sealings comprising a complex structure with multiple elements.